An example power supply configured for onboard use in a vehicle provides an AC output voltage, e.g., nominally set at 115 VAC or at 230 VAC. Conventionally, the power supply is off when the vehicle is off and on when the vehicle is on. A further refinement aims for reducing wasted power while the vehicle is on, by turning the power supply off if it is not being used.
In one example, the AC outlet of the power supply includes a mechanical arrangement that is actuated by insertion of the prongs of a power cord into the outlet. Such arrangements can be made reliable but suffer from at least two drawbacks. First, mechanical detection of plug insertion adds significant design and manufacturing complexity to the outlet. Second, mechanical detection of the plug is not equivalent to detecting whether there is an electrical load attached to the outlet. Plugging in an extension cord with nothing plugged into its other end triggers the mechanical detection as surely as plugging in a laptop computer or other electrical load.
Other approaches may rely on higher-level data communications to enable and disable the power supply, e.g., involving messages carried on one or more information busses within the vehicle. To the extent that the designer of a power supply might aim for actual detection of the loading on the AC outlet, that approach raises a complex mix of challenges relating to safety-of-design, reliability, and complexity.